With today's energy costs and the need to reduce emissions, the release of a water steam to the atmosphere becomes a wasteful and non-economical practice. Therefore, every facility strives to recycle as much water, steam and heat as much as possible.
In current industry Steam Assisted Gravity Drainage (SAGD) facilities the produced water from the oil/water separation first sent to produced water coolers. The purpose of these coolers is to cool the water to well below the flash point (to a temperature of approximately 80° C.) before the water is further treated to ensure that no flashing will occur downstream of the coolers. After cooling, the produced water is typically sent to a skim oil tank, then to an Induced Gas Floatation (IGF) unit and finally to an Oil Removal Filter (ORF). These serve to remove trace oil from the water before it is sent to an evaporator or warm lime softener.
There are a few issues with the current industry practice. The produced water coolers in most SAGD facilities have been found to be a high fouling service. These exchangers can cause serious maintenance issues with the requiring manual cleaning on a weekly basis. The manual cleaning of the exchangers is a labor intensive process and also poses health and safety (HSE) issues. In order to manually clean the exchanger while maintaining production, spare exchangers with their associated piping and valves are generally installed. Manual cleanings can be minimized but not eliminated through use of online cleanings.
Further the water must be reheated prior to introduction into downstream water treatment (hot/warm lime softening or evaporator). This cooling and reheating of the water increases the capital, operating and maintenance costs of a facility.
The process of using produced water coolers to eliminate flashing has been used since the first SAGD facility was designed. The industry has tried to tackle the high fouling issues with limited success and has turned to trying to more effectively clean the fouling from the exchanger. The industry has looked at the design of the exchangers and the operating conditions to try to maintain the produced water stream at as high a temperature as possible. The exchanger fouling has been seen to increase with a decrease in outlet temperature of the process stream.
Processors have also looked at ways of cleaning the exchanger while still in service. This has been attempted by running a high temperature stream through the exchanger to remove the fouling by re-dissolving the deposit into solution. These solutions have decreased the maintenance required on the exchangers and lengthened the time between shutdowns of the equipment, but have not solved the fouling problem.
There is therefore, still a need in the industry for a better solution for water treatment unit, which requires less maintenance due to fouling, is economical to operate and at the same time prevents flashing later in the process.
The objective of this invention is to provide a system which reduces the maintenance costs of a facility by devising a way to eliminate the high fouling produced water exchangers.
Another objective of this invention is to reduce the capital and operating costs of the facility by having the produced water entering the downstream equipment as hot as possible and minimize the reheating equipment. This results in less energy being used to re-heat the water later in the process.
Lastly, the produced water coolers are generally multiple shell and tube exchangers. These are relatively expensive pieces of equipment. There is an opportunity to reduce the capital cost of the facility by eliminating this equipment.
Other benefits and features of the invention would be apparent to the person skilled in the art from review of the following claims, drawings and descriptions of the preferred embodiments.